Expanding waistlines are not just tipping scales but may also push the mercury higher around the world, according to a new study.
As humanity becomes more rotund, more resources are needed to cool, nourish and transport the extra weight, a trend that can contribute to climate change by requiring the consumption of more fossil fuels and resulting in more greenhouse gas emissions.
Emerging economies are nudging their way into this movement as they seek the trappings of modern prosperity -- personal cars, sedentary air-conditioned office jobs and fast-food -- through dirty energy. Now a paper published this week in BMC Public Health calculates how human populations have grown in number and size, teasing out how obesity contributes to human biomass and the extra energy needed to sustain that heft.
"Energy use is a function of the basal metabolic rate," the amount of energy an individual consumes at rest, explained Sarah Walpole, a practicing physician in the United Kingdom and a co-author of the study. "A heavier body needs more food to be sustained."
Carrying that extra weight means eating more, which means more food has to be produced, packaged, transported and refrigerated, increasing how much electricity and fuel is needed per person. Heavier bodies also need more fuel to move around as engines and motors strain under heavier loads. It makes intuitive sense, but how much of an impact does "fatness" actually have?
To find out, Walpole and her co-authors used data from the World Health Organization and the United Nations to calculate the average adult body mass in different countries. They also calculated physical activity levels controlling for age and gender.
North Americans hold the heavyweight title
The results showed the global average body mass was 62 kilograms (137 pounds), but in North America, the average was 80.7 kg (178 pounds) while in Asia it was 57.7 kg (112 pounds). Though North America is home to 6 percent of the world's population, it accounts for 34 percent of the world's human biomass due to obesity. On the other hand, Asia, home to 60 percent of the world's population, has 13 percent of obesity-related biomass.
And these numbers are only going up. Developing countries are emulating wealthier nations, consuming more energy, becoming less physically active and eating fattier foods en route to industrialization. "The whole population of the world is shifting [its lifestyle] to that of the United States," said Ian Roberts, a co-author and professor at London School of Hygiene and Tropical Medicine.
If the rest of the world ate, worked and lived like Americans, humanity's spare tire would swell by the equivalent mass of 935 million average-sized people and soak up the food, water and electricity of an additional 473 million adults, according to the report. This would mean the average adult would eat an additional 261 calories per day.
There are some robust contenders. Just behind the United States in the list of top 10 heaviest countries is Kuwait. Four other Middle Eastern nations also make the list, which Roberts attributes in part to low gasoline prices in these regions. Cheap fuel means people are more likely to use cars instead of their legs to move around, so their spare food energy is stored as fat.
Asians are the lightweight models
On the opposite end of the spectrum, the list of lightest countries is topped off by North Korea, followed by Cambodia, Burundi and Nepal. If Japan were the model for the entire world, global human biomass would shrink by 14.6 million metric tons, equal to 235 million people of average mass. Energy requirements would decrease as if there were 107 million fewer adults on the planet.
Roberts said the results indicate that conventional wisdom on aid and international development needs to be reassessed. "We don't feed mouths, we feed bodies. We feed flesh," he said, adding that the blame for resource scarcity and ecological degradation should be placed less on poor people having more children and more on the relatively wealthy living unhealthy and unsustainable lives.